如何在SQL中选择每个组的第n行

Question

I have a table like this

member_id	book_title
1	one-one
1	one-two
1	one-three
2	two-one
2	two-two
2	two-three

I want to group by member_id and 3rd book title, so if I run the query, the result must be:

member_id	book_title
1	one-three
2	two-three

Answer 1

Assuming with "3rd book title" you mean " the third book if sorted alphabetically by title " this can be achieved using window functions:

select member_id, book_title
from (
   select member_id, book_title, 
          row_number() over (partition by member_id order by book_title) as rn
   from the_table
) t
where rn = 3;

Note that this won't return members that have less than 3 books assigned.